The invention concerns a device for receiving and dispensing liquids, with a plurality of piston-cylinder units which are disposed on a piston plate and a cylinder plate, respectively, wherein the liquid is received and dispensed by displacing the pistons in the cylinders by changing the distance between the plates using a drive mechanism and a plate guidance, perpendicularly to the plate planes, wherein the volume can be determined by an upper and a lower stop, at least one of which can be adjusted using at least one adjusting means.
In modern biological research, high-throughput methods are increasingly used, i.e. mass processing of samples, which are nearly always associated with pipetting steps. The samples are processed in plates having 96, 384 or even 1563 depressions in a standardized format. The large number of necessary pipetting steps can practically no longer be dealt with using conventional manual 8 or 12 channel pipettes. For this reason, pipetting automats having 96 or 384 channels are used (Beckman-Coulter, Gilson, Tecan, Zymark, Quiagen, Robbins, Zinsser, Perkin Elmer etc.). These devices are, however, extremely expensive, require a large amount of floor space and a large number of staff for programming, operating and maintenance. The piston unit of these automated pipetting systems is moved parallel upwards and downwards with extreme accuracy by rapidly rotating spindle drives. Stopping at a defined Z position exactly defines the pipetting volume.
A spindle drive of this type, having the required rapid and precise simultaneous spindle speed, is inappropriate for a pipetting system which is operated manually or with a simple drive, since either the mechanical devices or the control and drive are excessively complex or expensive.
U.S. Pat. No. 5,540,889 discloses a simple mechanical device having the features of the above-mentioned type. In this device, the piston plate is moved relative to the cylinder plate by a manual drive rod mounted to the center of the piston plate. An adjustable stop for presetting the pipetting volume is provided on the manual drive rod. The parallelism between the piston plate and the cylinder plate is thereby achieved by the manual drive rod guidance and optionally also by the piston guidance in the cylinders. This principle corresponds to the conventional multi-channel pipettes (the above-mentioned 8 or 12-channel pipettes). U.S. Pat. No. 5,540,889 defines the term “microvolume” as a volume on the order of a microliter in a range between about ½ microliter to 10 microliters. However, this mechanism of prior art is deficient with regard to handling such very precise volumes during pipetting, since these guidances cannot guarantee absolute parallelism and thereby exactly identical volumes of the liquid to be pipetted, compared to the controlled spindle drives of the above-mentioned automatic units, wherein excessive expense to ensure exact plate guidance would, in turn, be uneconomical. This problem increases with the number of piston-cylinder units and thereby with the size of the plates, such that these guidances can simultaneously operate either only a few piston-cylinder units or volume accuracy is not possible.
It is therefore the underlying purpose of the invention to modify a device of the above-mentioned type in such a manner that it is suitable for handling very precise volumes of a larger number of piston-cylinder units with little technical difficulty.